Most methods of fabricating DRAM trench storage nodes use silicon as a trench conductor material. As the trenches get deeper and achieve a higher aspect ratio, it requires more time to access the stored charge in the trench. It is difficult to use more conductive materials, such as aluminum, copper or platinum, in the trench due to the high thermal cycles that are required in the dynamic random access memory (DRAM) device fabrication.
Carbon nanotubes have recently attracted attention for use in very high-density integrated circuit devices. For example, U.S. Pat. No. 6,515,325 describes a vertical transistor and capacitor cell using a single nanotube to form a device. U.S. Pat. No. 6,566,704 describes a transistor including vertical nanotubes in which the source and drain are respectively formed at lower and upper parts of the nanotubes. These patents also describe processes for growing a nanotube on a substrate, where the nanotube is grown upwards from the substrate.
In order to employ carbon nanotubes in a trench-type capacitor memory device, it is necessary to form the nanotubes in a structure suitable for a storage node trench. This in turn requires that the nanotubes be grown down into the trench. The present invention addresses this problem.